Method for improving bond between transplanted coating and die-casting

ABSTRACT

An improved process is disclosed for uniting an electrolytically deposited cermet with a molten cast material such as aluminum. The cermet is deposited on a mandrel so as to provide a smooth inner surface (8-12 r.m.s.) and a controlled rough outer surface at least 250 times more rough than the inner surface. Electrolytically deposited copper is positioned on the cermet and assumes the rough character of said cermet outer surface. The assembly of electrolytic deposits is then placed in a die-cast machine where molten metal, such as aluminum, is cast thereabout to form an integrated composite particularly useful as a rotor housing for a rotary internal combustion engine.

United States Patent [191 Cordone METHOD FOR IMPROVING BOND BETWEENTRANSPLANTED COATING AND DIE-CASTING [75] Inventor: Leonard G. Cordone,Allen Park,

Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: Aug. 20, 1973 [21] Appl. No.: 390,134

[52] US. Cl. 164/98; 29/527.3; 164/9;

164/46; 164/95; 204/40; 204/49 [51] Int. C1. B22D 19/02 [58] Field ofSearch 164/19, 20, 59, 69, 94,

[56] References Cited UNITED STATES PATENTS 2,911,708 11/1959 Fike et a129/527.3

3,061,525 10/1962 Grazen 204/49 3,083,424 4/1963 Bauer 164/112 X3,098,270 7/1963 Bauer 164/112 X 3,293,109 12/1966 Luce et a1. 204/38 E3,616,288 10/1971 Snauely 204/26 3,628,237 12/1971 Zeigler 29/527.63,640,799 2/1972 Stephan et a1. 204/40 3,797,101 3/1974 Bauer 164/463,856,635 12/1974 Brown 29/527.3 3,878,880 4/1975 Jones 164/9 FOREIGNPATENTS OR APPLICATIONS 873,012 7/1961 United Kingdom Nov. 25, 1975OTHER PUBLICATIONS Bonding Cast Iron to Aluminum Castings," Light MetalAge, Oct., 1959, p. 17.

Aluminum Bonded by Diecasting Process, Steel, Nov. 30, 1959, pp. 98l00.

Transplant Coated Aluminum Cylinder Bores, A. F. Bauer, Paper No. 369C,1961, Summer Meeting. Society of Automotive Engineers, 485 LexingtonAve., N.Y., NY.

Primary ExaminerRoy Lake Assistant ExaminerPaul A. Bell Attorney, Agent,or Firm-Joseph W. Malleck; Keith L. Zerschling [57] ABSTRACT An improvedprocess is disclosed for uniting an electrolytically deposited cermetwith a molten cast material such as aluminum. The cermet is deposited ona mandrel so as to provide a smooth inner surface (8-12 r.m.s.) and acontrolled rough outer surface at least 250 times more rough than theinner surface. Electrolytically deposited copper is positioned on thecermet and assumes the rough character of said cermet outer surface. Theassembly of electrolytic deposits is then placed in a die-cast machinewhere molten metal, such as aluminum, is cast thereabout to form anintegrated composite particularly useful as a rotor housing for a rotaryinternal combustion engine.

4 Claims, 2 Drawing Figures &

FIG.2

Sheet 2 of 2 METHOD FOR IMPROVING BOND BETWEEN TRANSPLANTED COATING ANDDIE-CASTING BACKGROUND OF THE INVENTION Electrolytic deposition createsa non-porous dense material by the inherent characteristic ofelectrolytic deposition which deposits the coating atom by atom.However, it is difficult to adhere another different material to theelectrolytic deposit of material because of such density andnon-porosity. This has not been a severe problem heretofore sinceelectrolytically deposited metals have rarely been used as functionalparts, but rather as decorative outer coatings. However, it has beenfound that in a rotor housing for a rotary internal combustion engine,an electrolytic layer of considerable thickness can impart certaindesirable characteristics, the most important of which is wearresistance.

Under the present state of art, there is a tendency for an electrolyticcoating to become disunited from a different substrate during severeservice it will receive in a rotary engine. The typical bond that mayexist between thin decorating electrolytic coatings and substrates, doesnot exist when dealing with thicker functional coatings. The environmentof such an engine imparts stress as well as heat fatigue, requiring astrong adherency between the exposed electrolytically deposited coatingand the supporting cast material. Because a typical rotor housing has anintricate configuration such as an epitrochoid, there is no opportunityto apply a combination of heat and pressure to achieve a conventionalmetallurgical bond. Also, the molten aluminum is not sufficient to wet acermet (such as nickel and silicon carbide) which under othercircumstances would provide a metallurgical bond by heat alone.

SUMMARY OF THE INVENTION The primary object of this invention is toprovide an improved union between differential materials which areparticularly used in forming a composite for a rotor housing of a rotaryinternal combustion engine.

A particular object of this invention is to provide a method whichfirstly controls the surface roughness of an electrolytically depositedcermet and secondly utilizes an electrolytically deposited intermediatemetal to assume a mirror image of the rough surface cermet whileresponding to the heat of molten material thereabout to effect amutually soluble metallurgical bond.

A specific feature of the inventive method comprises use of anelectrolytically deposited copper-based strike which is interposedbetween an electrolytically deposited cermet material (such asnickel-silicon carbide) and a molten cast material (such as aluminum oraluminum-based alloys).

SUMMARY OF THE DRAWINGS FIG. 1 is a schematic flow diagram of the stepsinvolved in a preferred method embodiment; and

FIG. 2 is a schematic illustration of a section of a composite coatedassembly comprising the constituents of this invention and illustratingthe view solidification structure.

DETAILED DESCRIPTION Turning now to the schematic flow diagram of FIG.1, a preferred sequence is illustrated. In Step I, a mandrel I isprepared from a suitable core material capable of being machined to avery exact complex configuration, such as an epitrochoid surface 11. Theepitrochoid surface is required by the internal wall of a rotor housingfor a rotary internal combustion engine. The epitrochoid surface 11 is amirror image of the resultant epitrochoid surface to be structured onthe rotor housing of the engine. A suitable material for this purpose isa chrome-bearing steel having a chromium content in the range of 3-25percent. The chrome content enables the material to be passivatedthereby facilitating non-adhesion between the mandrel and the materialto be deposited thereover. In addition, the mandrel may be tapered in adirection from one end to the other to facilitate stripping subsequentto Step 4. The surface 11 must have a surface roughness of 4-12 r.m.s.which may be imparted by machining and polishing.

In Step 2, the mandrel is placed in an electrolyte for the purpose ofelectrolytically depositing a cermet coating consisting of nickel withcarbide particles. The cermet may also be constituted of a base materialselected from either iron or a copper alloy and containing ceramicparticles selected from the group consisting of silicon carbide,tungsten carbide, oxides of aluminum or iron and diamond. The resultantelectrolytic coating will define a sleeve 12 about the mandrel. Thecomposition of the electrolyte for depositing the nickel-based cermet isnot critical, however, the following range of ingredients has been foundto be conveniently controlled: Ni So 7 H O in the range of -300 gramsper liter, Ni Cl 6 H O in the range of 30-70 grams per liter, and H B0in the range of 20-40 grams per liter. Silicon carbide, being among thehardest materials, is preferred because it combines high hardness withlow cost in a most desirable manner. The hard particles are introducedto the electrolyte in an amount in the range of l00-l50 grams per literand in a particle size range of 0l0 microns; the particles are helddispersed in the electrolyte by agitation. A PH value for theelectrolyte is selected according to other process variables and may bebetween 1 and 7 in a conventional manner. The temperature of theelectrolyte may be about F. The current density is sequentially stagedto be in the range of about 50-100 amps per square foot for a fewstarting moments of the deposition step and then eventually raised to500-1000 amps per square foot for the remainder of Step 2. Electrolyticnickel is the preferred anode material.

The deposited coating 12 is in the thickness range of 0.01-0.04 inches,preferably 0.025 inch, and has a porosity of substantially zero. This isin high contrast to the characteristic porosity of a spray coating whichhas a minimum of 5 percent. The porosity of a spray coating isdetrimental to heat transfer and forms a barrier at the very location inthe rotor housing where heat must be transmitted. The lack of porosityand the denser material affords a greater heat transfer. The outersurface 120 has a roughness controlled to be at least 250 times morerough than the mandrel surface 11 and thereby also the inner side 12b.More particularly, the roughness may be characterized by projections ofa height of at least 0.030 inches and concentrated so as to number 5-100per square cm.

The eventual casting of aluminum directly about such a coating 12encounters certain problems. The surface tension of aluminum isconsiderably high and must be lowered to effectively wet ormetallurgically adhere to the non-porous coating 12. One technique usedby the prior art is to use sand blasting to lower such surface tensionby creating a highly rough surface 3 for the coating. However, this hasnot proved successful because of cost and lack of control. A principalfeature of this invention is to utilize an intermetallic strike 13 overthe coating 12 which not only acts as a more satisfactory wetting agentfor the aluminum (since it is selected to be mutually soluble at castingtemperatures with aluminum) but also effects a limited degree ofalloying with the cermet material. The intermetallic strike should havea melting temperature below the cast metal, be mutually soluble in thecast metal, be easily electroplated, and have a coefficient of thermalexpansion slightly less (differ by only 4 micro-inches) than the castmetal.

In Step 3, the mandrel and sleeve coating 12 is placed in anotherelectrolyte to preferably receive coating 13 of elemental copper. Theelectrolyte bath may be constituted of (a) copper sulphate in theconcentration of about 28 ozs. per gallon, (b) concentrated sulphuricacid in a concentration of about 7 02s. per gallon. The bath ismaintained at a temperature in the range of 70-75F and a current densityis applied to the electrolyte in the range of 40-60 amps per square footand preferably 50 amps per square foot. The layer or coating 13, being acopper base constituent, is mutually 501- I uble with aluminum which isto subsequently cast thereabout. Coating 13 at both sides 13a and 13bassumes the controlled rough surface contours of side 12a to enhance thewetting characteristic of the aluminum against the upper coating. Thecopper coating is deposited uniformly but becomes a mirror image, of therough cermet surface 120. The copper coating is deposited in the:thickness range of 0.0005 to 0.002 inches, preferably 0.0005 inches.

In Step 4, the two electrolytic coatings and the mandrel are placed asan assembly into a die-cast machine 14 having a suitable cavity 15 whichis complimentary in shape to the outer coating 13. An aluminum-basedalloy is injected into the molding cavity about the assembly to form acasting 16 which is metallurgically bonded to the coating 13. The heatof the casting material penetrates the coating 13 to effect alloyingbetween the copper and nickel-silicon carbide coating. Thealuminum-based alloy may contain an amount of silicon (4-16 percent,preferably 10% Si and 3% copper). The cast metal is selected from thegroup consisting of aluminum or aluminum alloys, iron and magnesium.

' per strike or coating 13 by the mechanical interlock of the matingrough interfaces and by the alloying zone 17 where substantial amountsof aluminum and copper became mutuallysoluble. The copper strike hasrough sides 13a and 13b due to being uniformly deposited on roughsurface 12a of the cermet-12. The inner surface 12b of the cermet has anextremely smooth (4-12 r.m.s.) wear-resistance surface because itdeposited against the polished mandrel surface.

I claim as my invention:

1. A process for uniting an electrolytically deposited cermet with adie-cast metal, said cermet being comprised of a material selected fromthe group consisting of titanium carbide, tungsten carbide and aluminumoxide, said die-cast metal being selected from the group consisting ofaluminum, iron and magnesium, the process consisting of electroplatingsaid cermet in a thickness range of 0010-0040 inches, and having acontrolled surface roughness at one side, said cermet being 2. A processfor uniting an electrolytically deposited I cermet on a mandrel with adie-cast molten material, said cermet having a thickness in the range of0010-0040 inches, the improvement in saidprocess consisting ofelectroplating a copper-based constituent onto said cermet-mandrelassembly and subsequently casting said molten metal about said assembly,said constituent and die-cast molten material each having coefficientsof thermal expansion which differ by no greater than 4microinches/in./in./F, said copperbased constituent having a controlledsurface roughness at both sides thereof at least 250 times the surfaceroughness of the cermet surface facing said mandrel,

the resultant structure having both a mechanical and metallurgical bondbetween said copper and cast material as well as between the copper andelectrolytically deposited cermet.

3. A method of uniting an electrolytically deposited cermet with a castmetallic material, said union being particularly useful in a coatedrotor housing of a rotary internal. combustion engine, the. processcomprising;

a. defining a conductive mandrel having an outer sur-' facecomplimentary to the resultant inner surface of the union and having asurface roughness no greater than 12 r.m.s.,. b. electrolyticallydepositing a thin coating of a composite particle wear-resistantmaterial on to said mandrel, the current density applied to promote saiddeposition, being above 400 amps/ft during a substantial portion of thetime of said deposition, c. electrolytically depositing a coating of acopperbase constituent on to said wear-resistant material having athickness less than said wear-resistant material,

d. casting a molten metallic material about said assembly, the moltenmaterial having a coefficient of thermal expansion greater than thethermal expansion of said cermet, and

e. stripping said mandrel from said casting and inner coatings to exposethe inner surface of said wearresistant material.

4. The method as in claim 3, in which the cermet material is comprisedof nickel with uniformly and finely dispersed particles of siliconcarbide, andthe molten I cast material consists of an aluminum-basedalloy.

1. A PROCESS FOR UNITING AN ELECTROLYTICALLY DEPOSITED CERMET WITH ADIE-CAST METAL, SAID CERMET BEING COMPOSED OF A MATERIAL SELECTED FROMTHE GRUP CONSISTING OF TITANIUM CARBIDE, TUNGSTEN CARBIDE AND ALUMINUMOXIDE, SAID DIE-CAST METAL BEING SELECTED FROM THE GROUP CONSISTING OFALUMINUM, IRON AND MAGNESIUM, THE PROCESS CONSISTING OF ELECTROPLATINGSAID CERMET IN A THICKNESS EARGE OR 0.010-0.040 INCHES, AHD HING ACONTROLLED SURFACE ROUGHNESS AT ONE SIDE, SAID CERMET BEINGELECTROLYTICALLY DEPOSITED WITH A CURRENT DENSITY ABOUT 400 AMPS/FT2DURING A SUBSTANTIAL PORTION OF THE TIME OF SAID DEPOSITION, ANDELECTROPLATING A UNIFORM DEPOSIT OF COPPER-BASE CONSTITUENTS ONTO SAIDONE SIDE OF SAID CERMET IN A THICKNESS RANGE OF 0.0005-0.002 INCHES TOFORM AN ELECTROLYTIC-METALLURGICAL BONDED ASSEMBLY, AND SYBSQUENTLYDIE-CASTING SAID MOLTEN METAL ABOUT SAID ASSEMBLY WHEREBY THE HEAT OFSAID MOLTEN METAL IS EFFECTIVE TO CREATE AN ALLOY METALLURGICAL BOND 2.A process for uniting an electrolytically deposited cermet on a mandrelwith a die-cast molten material, said cermet having a thickness in therange of 0.010-0.040 inches, the improvement in said process consistingof electroplating a copper-based constituent onto said cermet-mandrelassembly and subsequently casting said molten metal about said assembly,said constituent and die-cast molten material each having coefficientsof thermal expansion which differ by no greater than 4microinches/in./in./*F, said copper-based constituent having acontrolled surface roughness at both sides thereof at least 250 timesthe surface roughness of the cermet surface facing said mandrel, theresultant structure having both a mechanical and metallurgical bondbetween said copper and cast material as well as between the copper andelectrolytically deposited cermet.
 3. A method of uniting anelectrolytically deposited cermet with a cast metallic material, saidunion being particularly useful in a coated rotor housing of a rotaryinternal combustion engine, the process comprising: a. defining aconductive mandrel having an outer surface complimentary to theresultant inner surface of the union and having a surface roughness nogreater than 12 r.m.s., b. electrolytically depositing a thin coating ofa composite particle wear-resistant material on to said mandrel, thecurrent density applied to promote said deposition, being above 400amps/ft2 during a substantial portion of the time of said deposition, c.electrolytically depositing a coating of a copper-base constituent on tosaid wear-resistant material having a thickness less than saidwear-resistant material, d. casting a molten metallic material aboutsaid assembly, the molten material having a coefficient of thermalexpansion greater than the thermal expansion of said cermet, and e.stripping said mandrel from said casting and inner coatings to exposethe inner surface of said wear-resistant material.
 4. The method as inclaim 3, in which the cermet material is comprised of nickel withuniformly and finely dispersed particles of silicon carbide, and themolten cast material consists of an aluminum-based alloy.